Direction finding system



March 9, 1943. H. e. BUSIGNIES ETAL DIRECTION FINDING SYSTEM Fi'led Aug. 1, 1941 M m r N 4 a x 1 N m U m E f 8 N ew W mg M W an 0 mm w wf H Mm #A Patented Mar. 9, 1943 asiaoii nmnorion FINDING SYSTEM Henri .G. Busignies; Forest Hill Boonton, Federal Telephone &

corporation of Delaware G. Richardson,

Newark, N. J-, a

Sr N- an Av r N- u s isnqrs Radio Corporation,

Application August 1, 1941 -Seria'l No. 404,998

4 Claims.-

our invention relates to improvements in radio direction finders, and particularly to that type of direction finder which employs additional antenna means for indicating the sense of the direction determined.

It is an object of the invention to provide a direction finder of extreme of a plurality of frequencies band. 7

Another object is to provide means for compensating for unbalancing of phase and ampli= tude relations in direction finding antennae due to field distortion, mechanical inequalities, or weather conditions or different electrical characteristics of the antennae'and circuits used.

A further object is' to provideimprovedmeans for combining voltages induced in a loop antenna with those picked up by a sense antenna for obtaining accurate directional sense indications;

Other objects and various further featuresof Within a rather large novelty and invention will hereinafter be pointed out or will become" apparent from a reading of the following specification in" conjunction with the drawing included herewith. In said draw ns; v

Fig. 1 is a schematic circuit diagram of a direction finder circuit in accordance with theinvention;

Fig. 2 shows a schematic perspective view of,

an embodiment of Fig. 1; and n V n Fig. 315 a graphicalshowin'g of characteristics of portions of the circuit of Fig. 1.

a portion of the apparatuso f It' is well known that a rotatable loop antenna used for direction finding" purposes] and also: that this type of antenna is incapable of itself to discriminate between two senses'180? the familiar 180 course'or apart; Accordingly, direction ambiguity that this 180 I employing additionally a non -dire'ctivetype anre'sult'si It ha'sibeen found tenna' and superimposing energy picked" up energy received" by the loop thereby upon t -fin t. a

However, the addition of thenon-directive or sense antenna does not* of itself seem to" solve" all the problems connected with highly accurate radio-goniometry. Since the voltages received by" the'directionalor loop antenna are 90 out of phase with those induced inthe senseanten'na', phaseshifting means are necessary toconditi'on both these induced voltages for superposition;

Furthermore, the associated circuits of' diiferent electrical char; acteristics' has been found to give'rise'to detriaccuracy at any one ambiguity may be eliminated by use of: several antennae" and voltage to appear in t mental phase" shifts relative to each other over a frequency band. Thiseffect, together with small loopantennae unbalance, causes a small e loop antenna out of phase with the desired and normally received energy. Such-avoltage necessarily causes a blurring of the minimum, thereby increasing the difficulty of taking" bearings and reducing ac; curacy. To neutralize the undesired voltage'a balancing voltage out of phase with the desired voltage in-theloop must be supplied. This balancing voltage may be obtained directly from the sense antenna (since it receives energy 90 out of phase with the loop antenna), fror'n' a separate; source appropna the v loop antenna itself correction, of course) n V In actual practiceit is relatively difficult to perform either or" both of the above-indicated compensation functions; This difiiculty will be apparentfrom anappreciation of the obviously diiferent characteristics ofloop and sense antennae, If an Adcock spaced antenna unit is employedinstead of a loop; the goniometer cir cuits associatedtherewith involve s'uch diiferent impedance and other characteristics as further to complicate performance of the compensating functions; addition there are difiiculties en'- c'ou'nt'ered' in thedejsign of a phase shifting circuit which will givea constant shift and at the same timekeeprelative'" phase transmission constant' for any frequency band. V

Accordingly, the invention proposes novel means'for ameliorating these problems; fe'rred embodiment of such schematically in' Fig 1. This drawing shows direction finder equipment including direction sensitive antenna means Iil'and non-directional or' sense antenna means ii antenna meansjlocomprises' a loop rotatable about a generally ver'ti'caljaxis i2; In a known manner, energy received by loop I0 is relayed to a receiver 13; and detected'output'energy is then fed to appropriate "indicating 'means I 4.

Enrgy'reea ed (with appropriate phase means is included 74 1 e ve I 1. Preferably; line I! has low impedance charly phased, or from' within a rather large A pre- In the form shown dftenergy may then be and, in accordance with acteristics and is so wound or otherwise constructed that it longitudinally progressively shifts the phase of input energy a half, or even a full, wave length.

Sense energy for direct superposition upon that received by loop It! may be derived by induction from line H by coil means 18. It is contemplated that there will be relatively little inductive linkage between coil l8 and line I! so that coil l8 will not draw so much energy from the line as substantially to affect the progres sive phase shifting character of the latter. Coil I8 is preferably slidable longitudinally of line H v to permit appropriate phase shifting adjustment of sense voltage for a particular frequency before superposition upon the loop voltage.

Since, for a given displacement of coil 18, the phase shift caused by the transmission line varies loop energy. Control means 30 may be provided in the case of coil 29 in order to vary the magnitude of the balancing voltage as required to neutralize the undesired parasitic voltage effects.

The displacement of coil 29 may be controlled in a manner similar to that of coil 18. To this end, a drum 23 winds a line 32 in accordance with rotary movement of the gang of tuning condensers in the receiver. Line 32 is fixed to coil 29, and the latter is held firmly in place by resilient retaining means 33. Since the phase shift which must be kept constant for coil 29 is greater than for coil I8, corresponding displacements of these coils will be greater for coil 29 (see Fig. 3). Accordingly, drum 23 should be made larger than drum 22, and cam 2| may still serve to effect the appropriate compensation for non-linearity, as

- will be clear.

with the frequency of the received signal, coil [8 l must be displaced along serve a constant phase shift of sense energy with respect to loop energy over a frequency band. This displacement may be accomplished automatically by means coupled to, say the shaft operating the receiver tuning condensers. A schematic arrangement of such a mechanical device is shown in Fig. 2, in which coil l8 will be recog nized as slidably disposed .with respect to line I! along a guide rail I9.

In Fig. 2 a rotatable shaft 29 is coupled to the tuning condenser shaft (not shown) as above indicated and drives cam means 2i and a pair of drums 22, 23. Drum 22 bears a line 24 which is secured thereto at one end and at the other to coil [9. If desired, and preferably, spring or other tensioning means 25 may be provided securely to retain coil l8 at any particular position along the length of line H. It is clear that with the apparatus thus far described coil I8 is given a translatory motion as the receiver is tuned to a particular signal frequency and that a corresponding phaseshift results.

However, it has been found that the relationship between such displacement and frequency for constant phase shift is not necessarily linear. This fact is clearly shown in the graphical representationof these quantities in Fig. 3. It will be seen, for example, that for a constant phase shift of 90 in a range of frequencies F to 2F, the necessary displacement of coil I8 is much less than it would be for a constant phase shift of 180, and so on. Accordingly, we provide additional means to account for this non-linearity. In the form shown this means comprises an additional control as to the displacement of line 24. A cam follower 26 rides cam 21 and imparts displacement motion to a sliding bar 21. Bar 21 rigidly displaces idler pulley 28, which in turn engages line 24. By proper design of cam 2| and choice of diameter of drum 22, appropriate desired motion may be imparted to coil i 8, as will be clear. It thus appears that automatic compensation of phase between 'the sense and loop antennae may bemade as the receiver'is being tuned.

It was shown abovethat unwanted phase variations may occur between the voltage induced in the loop and that induced in the sense antenna, and that to neutralize these unwanted effects a voltage 90 out of phase with that induced in the loop is required. It is proposed in accordance with the invention that another coil 29 similarto coil [8, be slidably order to perform the correct phase. As in disposed along line H in balancing function at the the line in order to prethe case of coil l8, energyinduced in coil 29 is relayed forsupe rposition upon In accordance with common practice the device shown in Fig. 1 is intended for separate operation in the determination ofdirectivity or-sense. Accordingly, we provide switching means 3| for alternately feeding receiver l3 withproperly compensated signal energytion and compensated energy for sense determination. In the form shown switch means-3l is double-pole double-throw andalternately connects coil l8 or coil 29 to the loop antenna In some cases, relay means may prove desirable for performing the switching function, as will be clear.

While the coils l8 and 29 have been shown as directly connected to the loop antenna, which in turn directly feeds receiver l3, it is to be understood that in certain cases other forms of coupling will be found preferable. -For example, energy from either of coils l8 or 29 may be inductively coupled to the coil of the radio frequency tank circuit of the receiver in a, known manner. Loop energy may,.of course,-be fed by a similar coupling to the receiver.

It is clear that we have described, a relatively simple structure for automatically setting direction finding apparatus to be critically accurate and sensitive at any frequency within a large band. Moreover, it is to be understood that, while the invention has been described in'detail in connection with a preferred form, various modifications, additions, made within its scope. What is claimed is: f s I 1. Ina radio direction finder systemcomprising directionally discriminating receiving an-.

tenna means coupled tov a receiver and non-directional responsive receiving antenna means,

means feeding energy received by said nondi-. rectional antenna means to said receiver, said feeding means comprising an artificial transmiss on hne having phase displacementcharacteristics progressing longitudinally thereof, a first coil inductively coupled to said artificial line and Ion-- gitudinally displaceable'therealong,a second coil inductively coupled to said artificial line and longitudinally displaceable feeding energy from said out of phasewith energy received by said directionalantenna means, and means for feeding energy from said second coil to said receiver in phase with energy received by said directional antenna means.

' 2. A radio direction finder system-comprising a receiver including tuning means, directionally discriminating. receiving antenna means coupled to said receiver, non-directionally responsive receiving antenna means, and means feeding-energy for directivity determina and omissions may be therealong, means-for first'coil to said receiver received by said non-directional antenna means to said receiver, said feeding means including an artificial transmission line having phase displacement characteristics progressing longitudinally thereof, coil means inductively coupled to said transmission line, and means coupling said tuning means and said coil means and displacing said coil means longitudinally of said transmission line in accordance with adjustment of said tuning means.

3. A direction finder according to claim 2, in which said coil means includes a first coil feeding energy to receiver in quadrature with that received by said directional antenna means, and a second coil feeding energy to said receiver in phase with that received by said directional antenna means, and switching means alternately supplying energy induced in said first coil and in said second coil to said receiver.

4. A direction finder according to claim 2, in which said coupling means includes cam means rotated by said tuning means, cam follower means, and means connecting said cam follower means and said coil means.

HENRI G. BUSIGNIES. AVERY G. RICHARDSON. 

